#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main()
{
    putchar('a'); // 标准IO
    write(1,"b",1); // 系统IO
    putchar('a');
    write(1,"b",1);
    putchar('a');
    write(1,"b",1);
    // bbbaaa
    exit(0);
}